Multifluid description of nonequilibrium plasmas

Summary form only given. A multifluid hydrodynamics description of a multispecies nonequilibrium reacting plasma, regarding each species of the plasma as a separate fluid coexisting with the fluids made up of other species, is widely employed, in particular in the theory of a glow discharge, of a near-cathode region of an arc discharge, of plasma edge in fusion devices, and of flows of the ionized air past re-entry vehicles. In order to give a self-consistent kinetic derivation of multifluid equations one should treat the Knudsen numbers characterizing collisions of particles of any species between themselves as small parameters and those characterizing collisions of particles of different species as parameters of order unity. Such a derivation is given in the present paper. The term of the Boltzmann equation for every species accounting for collisions with the particles of the same species is considered as leading, the terms accounting for collisions with the particles of other species are considered as small, along with the flow terms. The distribution function of each species in the first approximation is Maxwellian with its own mean velocity and temperature. Equations of continuity, momentum and energy for every species resulting in the framework of such an approach from the conventional Chapman-Enskog procedure coincide with those for a simple gas, presence of other species being taken into account in terms of external sources or sinks of mass, momentum, and energy. Explicit expressions describing these sources/sinks are obtained.